One problem that has historically plagued large volume mixing machines is known as "bowl creep". In these large volume mixing machines, a rotatable crank handle moves a mechanical screw, which raises and lowers a bowl support. Under the force of the beaters and the vibration of the mixer, there is a tendency for the screw, which raises and lowers the bowl support, to "unscrew" thereby allowing the support to lower and the bowl to move away from the beaters and the mixing position. The movement of the bowl away from the beaters often results in incomplete mixing of the ingredients in the mixing bowl.
To prevent the bowl support and, subsequently, the bowl from moving during the mixing operation, an operator will usually tie down the crank handle which is used to raise and lower the mixing bowl. Ropes, bungy cords, and the like have been used for this purpose. This method has not been entirely successful because it requires space to tie down the mixer handle which in turn hinders the operator's effective use of the mixing machine. Further, the mixer must be "untied" before new ingredients can be added to the mixing bowl or before the mixing bowl can be moved away from the mixing head.
Another method to prevent bowl "creep" is to reduce the lead angle and/or increase the thread angle of the screw in the gear train used to raise and lower the bowl support, so that a slight movement of the gear train causes a minute movement of the bowl support, i.e., little to no bowl "creep." However, a mixer incorporating this approach requires the operator to expend a great effort to raise the mixing bowl into position for a mixing operation. This approach is not desirable because it requires a large number of cranks on the handle used to raise and lower the bowl support to cause the bowl support to move a short distance toward the mixing head. Finally, as the mixing machine ages, as parts wear and as fasteners become loosened, bowl "creep" may still occur.
The current invention offers an improved mechanism to maintain the bowl support and, subsequently, the mixing bowl of a mixing machine in the proper operating position during a mixing operation.